I am looking around here for the engineering data but 2 years gone is a long time to keep things sorted. By memory, I think you can expect that cleaned up glass will have a lower bond strength by 20%-25% Just plain silicone adhesive to cured silicone adhesive is about 65% percent that of a new and clean bond.
Soon as I find all that data I will post. There is a lot of bad info out there.
One caveat. I am speaking only of Dow-Corning Silicone adhesives.